1. Field of the Invention
The present invention relates to an apparatus for disposing of fuel-vapor, especially to an apparatus, for disposing of fuel-vapor, which can control the air-fuel ratio of an exhaust gas within the proper range when a purge of fuel-vapor from a charcoal canister is initiated.
2. Description of the Related Arts
Fuel-vapor evaporated from a fuel tank is absorbed in a charcoal canister and is properly purged into an inlet pipe, as fuel, in order to improve fuel consumption and to avoid air pollution.
However, because the fuel-vapor purged from the charcoal canister disturbs the air-fuel control of an engine, a purge procedure which does not disturb the air-fuel control has been already proposed.
For example, in Unexamined Patent Publication (Kokai) No. 62-174557, a control apparatus for disposing of fuel-vapor which avoids exerting a harmful influence upon the air-fuel control by gradually opening or closing a purge valve at the beginning or the end of a purge operation, is disclosed.
Furthermore, in Unexamined Patent Publication (Kokai) No. 2-245461, a control apparatus for disposing of fuel-vapor which makes a valve opening speed slow, in accordance with a detected concentration of a purge gas, is disclosed.
As a degree of an influence which is exerted by a fuel-vapor purge is affected by the operating condition of the engine, it is unavoidable that the air-fuel ratio is affected by a purge if the opening or closing speed of a purge valve is kept constant.
Furthermore, because the concentration of a purge gas cannot be accurately detected at the start of a purge operation, an opening or closing speed of a purge valve cannot be accurately learned, and the air-fuel ratio may be affected by the fuel-vapor.